To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin is in a condition of 90 (EF), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins in lower conditions.

2. Current Starting Price and Previous Prices: The current starting price is 150 euros. In previous auctions, the average hammer price has been 120.49 euros, suggesting that the market has valued this coin in a similar range in the past.

3. Price Trends: By observing the hammer prices of coins with similar conditions (around 85-90), we can see that they have reached hammer prices that vary, but some have reached 200 euros or more in similar conditions.

4. Demand and Supply: The coin has been auctioned 51 times, with an 86% sell-through rate (44 out of 51). This indicates good demand in the market.

5. Recent Hammer Prices: In the most recent auctions, hammer prices have varied, but some have reached up to 290 euros in lower condition.

Based on these factors, an estimated maximum purchase price for this coin could be between 200 and 250 euros, considering its good condition and the price trend in previous auctions. However, since the starting price is 150 euros, it is likely that buyers will be willing to bid more, especially if there is interest in the coin.

Therefore, a reasonable maximum purchase price could be 250 euros.